Semiconductor memory card

ABSTRACT

A semiconductor package for a semiconductor chip, e.g., a memory chip, is disclosed. The semiconductor package includes a substrate having a generally rectangular perimeter with four sidewalls and a chamfer between adjacent first and second ones of the sidewalls. The memory chip is electrically coupled contacts provided on an opposite surface of the substrate. The contacts are in a row along only the one sidewall of the substrate. A body of a plastic encapsulant covers the first surface of the substrate, the memory chip, and at least two of the sidewalls of the package. The entire perimeter of the substrate, including all four sidewalls and the chamfer, are covered by the plastic encapsulant. Alternatively, only two or three of the sidewalls are covered by the plastic encapsulant, with the other sidewall(s) being exposed and vertically coplanar with a respective sidewall of the plastic encapsulant.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/656,253, entitled “Semiconductor Memory Cards And Method Of MakingSame” filed Sep. 6, 2000.

BACKGROUND

A. Technical Field:

This invention relates to packaging memory cards, such as flash or ROMmemory cards.

B. Related Art

A recent global spate of portable electronic devices such as computers,electronic toys, PDAs, cameras, smart phones, digital recorders, pagers,and such has spawned a concomitant need for compact, removable datastorage components. One response to this demand has been development ofso-called “memory cards.” Typically, a memory card contains at least oneor more semiconductor memory chips within a standardized enclosure thathas connectors thereon for electrical connection to external circuitry.Examples of these include so-called “PC Cards” and “MultiMediaCards”made in accordance with standards promulgated by such trade associationsas Personal Computer Memory Card International Association (“PCMCIA”)and MultiMediaCard Association (“MMCA”), respectively.

An exemplary embodiment of such a memory card, namely, a MultimediaCard10, is illustrated in top plan, cross-sectional side elevation, andbottom plan views of FIGS. 1-3, respectively. Card 10 illustrated hasstandardized dimensions of 32 mm long×24 mm wide×1.4 mm thick, andtypically includes a memory capacity of 2 to 32 megabits (“MB”) ofmemory, which is accessed through seven contacts 22 located on a bottomsurface of card 10 using, e.g., a standard serial port interface (“SPI”)interface. A simple chamfer 30 on one corner of card 10 preventsincorrect insertion of card 10 into a connector in a host device.

Memory card 10 comprises a rectangular substrate 12, such as a printedcircuit board (“PCB”), and one or more semiconductor memory dies or“chips” 14 mounted on and electrically connected thereto using, e.g., alayer 16 of adhesive and conventional wire bonds 18, respectively.Surface mounting passive components 20, e.g., resistors, may also bemounted on and connected to substrate 12. Contacts 22 are connectedthrough substrate 12 to memory circuits defined by foregoing componentsand serve as input-output terminals of card 10.

When components 14, 20 have been mounted on and connected to substrate12, chip 14 is protectively encapsulated by a “glob-topping” process. Aglob 24 of a viscous encapsulant is dispensed onto a top surface of chip14, allowed to flow over its sides to said surface of substrate 12, andcured to form a protective envelope over chip 14. An external cover orhousing 26 (shown by dotted outline in FIG. 1) of thin sheet metal orplastic is installed over substrate 12 assembly by embedding said topsurface of assembly in a bed 28 of an adhesive contained in housing 26.

While said foregoing method provides a useable memory product, it isalways desirable in a rapidly evolving market such as this to developnew fabrication methods that simplify a product, reduce its costs, andenhance its functionality.

SUMMARY

This invention provides methods for making a memory card, e.g., aMultiMediaCard, that eliminate a need for an external housing and aseparate encapsulation step, and that enables more memory to be packagedin a same size of card.

In one of said methods, a substrate having opposite first and secondsurfaces is provided. A memory die, or chip, is mounted on andelectrically connected to said first surface of said substrate, e.g., bywire bonding. Said second surface of said substrate is attached to afirst surface of a flat carrier sheet, e.g., an adhesive tape. In oneembodiment, a mold is placed on said first surface of said carrier sheetsuch that said chip and said first surface of said substrate areenclosed in a cavity defined by said mold and said carrier sheet. Saidchip and said first surface of said substrate are encapsulated in amonolithic body of hardened plastic, e.g., by injecting a fluid plastic,such as a filled liquid epoxy resin, into said cavity and curing saidresin to harden same. Completed cards are then detached from saidcarrier sheet for use.

Said methods eliminate a need for an external housing on said card and aseparate chip encapsulation step. These enable a reduction in cardheight, or incorporation of more memory chips in a card with astandardized height using die-stacking techniques. Said methods are welladapted to volume production techniques.

A better understanding of above and other features and advantages ofthis invention may be had from a consideration of a detailed descriptionbelow of some exemplary embodiments thereof, particularly if suchconsideration is made in conjunction with appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is top plan view of a prior art memory card, with separateexternal housing shown in dotted outline to reveal card details;

FIG. 2 is a cross-sectional side elevation view into said conventionalcard shown in FIG. 1, as revealed by a cross-section taken therein alonglines II-II;

FIG. 3 is a bottom plan view of said prior art card shown in FIGS. 1 and2;

FIG. 4 is a top plan view of an exemplary embodiment of a memory cardmade in accordance with a method of this invention;

FIG. 5 is a cross-sectional side elevation view into said card shown inFIG. 4, as revealed by a cross-section taken therein along lines V-V;

FIG. 6 is a bottom plan view of said card shown in FIGS. 4 and 5;

FIG. 7 is a top plan view of a plurality of memory card subassembliesconnected together in a strip form during fabrication and before beingencapsulated in accordance with a method of this invention;

FIG. 8 is a top plan view of said plurality of memory card subassembliesshown in FIG. 7 attached to an elongated carrier sheet after beingseparated and during encapsulation in accordance with a method of thisinvention;

FIG. 9 is a top plan view of said plurality of memory cardssubassemblies shown in FIG. 8 after being encapsulated;

FIG. 10 is a top plan view of a plurality of memory card subassembliesconnected together in a strip form during fabrication and before beingencapsulated in accordance with another method of this invention;

FIG. 11 is a top plan view of said plurality of memory cardsubassemblies shown in FIG. 10 attached to an elongated carrier sheetafter being separated and during encapsulation in accordance with amethod of this invention;

FIG. 12 is a top plan view of said plurality of memory cardssubassemblies shown in FIG. 11 after being encapsulated and singulated;

FIG. 13 is a cross-sectional side elevation view into a memory cardhaving two stacked chips in accordance with one embodiment of thisinvention;

FIG. 14 is an enlarged partial cross-sectional elevation view into saidmemory card shown in FIG. 4, as revealed by a cross-section takentherein along lines XIV-XIV; and,

FIG. 15 is an enlarged partial cross-sectional elevation view into oneof said memory cards shown in FIG. 12, as revealed by a cross-sectiontaken therein along lines XV-XV.

DETAILED DESCRIPTION

A memory card 110 made in accordance with one exemplary embodiment ofmethods of this invention is illustrated in top plan, cross-sectionalside elevation, and bottom plan views of FIGS. 4-6, respectively. InFIG. 1, a “mold cap,” or hardened plastic body 132 encapsulatingelectronic components 114 and 120 and top surface of substrate 112 isshown in dotted outline to reveal underlying detail. Cross-sectionalelevation view into card 110 of FIG. 5 is produced by taking a sectionin FIG. 4 along lines V-V. Top plan views of two alternative embodimentsof memory card 110 at various stages in its production are shown inFIGS. 7-9, and 10-12, respectively.

As may be seen by reference to FIGS. 4-6, memory card 110 is identicalin size and contains elements similar to those of prior art memory card10 illustrated in FIGS. 1-3. Similar elements in card 110 are referencedby similar reference numbers, plus 100. Novel card 110 comprises arectangular substrate 112, e.g., a PCB, having respective first andsecond surfaces 111 and 113 and a semiconductor memory chip 114 mountedon and electrically connected on first surface 111. Chip 114 is mountedon first surface 111 of substrate 112 with a layer 116 of adhesive andelectrically connected to said first surface with conventional wirebonds 118. Particular contents of memory card 110 and configuration ofexternal contacts 122 may vary depending on particular application. Forexample, a plurality of memory chips and passive components may be used,or passive components may be omitted, or memory management chips may beincluded, among other possibilities. Again, certain industry standardsapply in certain cases.

In another possible embodiment (not illustrated) chip 114 may be mountedon and electrically connected to first surface 111 of substrate 112using well known “flip chip,” or “C4” method of die-to-substrateattachment. In such mounting, it may be desirable to underfill a narrowspace between chip 114 and first surface 111 of substrate 112 with asolid insulative material, e.g., a hardened epoxy resin, in a knownmanner. Surface mounting passive components 120, e.g., resistors, mayalso be mounted on and electrically connected to first surface 111 ofsubstrate 112. As in prior art memory card 10, input-output contacts 122are located at an edge of bottom surface 113 of card 110, and a chamfer130 is provided on one corner thereof for one-way-only insertion of cardinto a host device connector.

However, comparing novel card 110 shown in FIGS. 4-6 with prior art card10 shown in FIGS. 1-3 also reveals some important differences. Forexample, thin metal or plastic external housing 26, bed 28 of adhesive,and glob-top encapsulation 24 over chip 14 of prior art card 10 arereplaced in novel card 110 by a single hardened plastic body 132 whichmore effectively encapsulates electronic components 114 and 120, andrespective first surface 111 and side walls 158 of substrate 112.Moreover, replacement of such former elements and manufacturingprocesses related thereto by said single latter element andencapsulation process frees up additional space H (see FIG. 5) in card110 above chip 114, namely, about 0.3 mm. This space can be used e.g.,to mount additional components. For example, as shown in FIG. 13, asecond memory chip 114 can be mounted on top of first-mounted memorychip 114 above and electrically connected to first surface 111 ofsubstrate 112 using die-stacking techniques disclosed in, e.g., U.S.application Ser. No. 09/536,574, filed Mar. 28, 2000, and assigned to anassignee hereof. This increases memory capacity of card 110 whileretaining said same, standard form factor.

Said methods for making memory card 110 shown in FIGS. 4-6, as describedbelow in connection with FIGS. 7-9, and 10-12, respectively, are readilyadapted to simultaneous production of a number of cards in an elongatedstrip form. However, such methods are easily extended to manufacture ofa single memory card 110, or alternatively, to simultaneous productionof a rectangular array thereof (not illustrated), e.g., a 4×4 array ofmemory cards 110.

Thus, one method includes providing a continuous substrate strip 134having opposite first and second surfaces 136, 138 and a plurality ofindividual chip-mounting sites 140 on said first surface thereof (seeFIG. 7). A memory chip 114 and additional passive components 120, ifany, are mounted on and electrically connected to first surface 136 ofstrip substrate 134 in corresponding ones of mounting sites 140, asdescribed above. Alternatively, a plurality of memory chips and passivedevices, or one or more memory devices and no passive devices, may bemounted on first surface 136 of strip substrate 134. Numbers and typesof memory chips and passive components are application specific, and notlimiting of this invention.

As illustrated in FIG. 7, after electronic components 114 and 120 aremounted on and electrically connected to corresponding ones of mountingsites 140 on first surface 136 of strip substrate 134, substrate 134 iscut along dotted lines 142 to divide assembled strip 134 into aplurality of individual substrate assemblies 144, each having acorresponding individual substrate 112. Respective second surfaces 138of each individual substrate assembly 144 are temporarily attached to afirst surface 146 of a flat carrier sheet 148 (see FIG. 8) such thatindividual assemblies 144 are attached to carrier sheet 148 in aspaced-apart relationship, as shown in FIG. 8. Carrier sheet 148 may bea plastic film with an adhesive thereon, or a polyimide film with anadhesive thereon.

Substrate assemblies 144 can be temporarily attached to carrier sheet148 with a “tacky,” i.e., partially cured, adhesive. It is desirablethat said adhesive form a seal between opposing second surfaces 138 ofindividual substrate assemblies 144 and first surface 146 of carriersheet 148 to prevent encapsulant from entering between said opposingsurfaces during an encapsulation procedure. Said adhesive may be of aknown type that is initially tacky but which loses adhesion when exposedto ultraviolet (“U.V.”) light. In such an embodiment, subsequentdetachment of parts from carrier sheet 148 comprises exposing saidadhesive to ultraviolet light and lifting said parts away from sheet148.

When substrate assemblies 144 are attached to carrier sheet 148, each ofchips 114, corresponding wire bonds 118, and corresponding chip-mountingsites 140 are encapsulated in a monolithic body 132 of hardened plastic(see FIGS. 4-6). This can be effected in a number of different ways. Asshown in FIG. 8, a mold 150 (shown by dashed outline) having a pluralityof cavities 152 therein is placed on first surface 146 of carrier sheet148 such that each individual substrate assembly 144 is enclosed in aseparate corresponding cavity 152 between mold 150 and carrier sheet148. Carrier sheet 148 may be provided with a plurality of tooling holes154 for appropriate relative alignment of substrate assemblies 144 withmold cavities 152. Cavities 152 are each filled with a fluid plastic,e.g., an epoxy resin, and said resin is cured to harden same. Whenencapsulation is complete, mold 150 is removed from carrier sheet 148 toleave a plurality of completed memory cards 110 attached thereto, asshown in FIG. 9. Completed memory cards 110 are then detached fromcarrier sheet 148 for, e.g., post-encapsulation testing and packaging.

It may be noted in FIGS. 4-6 that side walls 156 of plastic body 132 arespaced outside of corresponding side walls 158 of respective individualsubstrates 112 (see enlarged section of FIG. 14), which results frominterior side walls 160 of mold cavities 152 being positioned outside ofside walls 158 of respective individual substrates 112 duringencapsulation (see FIG. 8). However, in other possible embodiments, oneor more of corresponding respective side walls 156 and 158 of plasticbody 132 and respective individual substrates 112 may be coplanar, asshown in FIG. 15 and described in more detail below.

In an alternative embodiment illustrated in FIGS. 10-12, a memory chip114 and additional passive components 120, if any, are mounted on andelectrically connected to first surface 136 of strip substrate 134 incorresponding ones of chip-mounting sites 140, as described above, toform a single strip assembly 162 (FIG. 10). However, strip substrate 134is not divided into individual assemblies, as above. Instead, secondsurface 138 of undivided strip assembly 162 is then attached to firstsurface 146 of carrier sheet 148, and memory chips 114, passivecomponents 120, and at least first surface 136 of strip assembly 162 areencapsulated in a single monolithic body 132 of hardened plastic, asfollows.

As shown in FIG. 11, a mold 164 having a single cavity therein is placedon first surface 146 of carrier sheet 148 such that at least firstsurface 136 of substrate strip assembly 162, including chips 114 andpassive components 120, are enclosed in cavity 166 between mold 164 andcarrier sheet 148. Cavity 166 is then filled with a fluid plastic, andsaid plastic is hardened into a single-piece plastic body 132 (see FIG.11).

When plastic body 132 is hardened, mold 164 is removed from carriersheet 148, and plastic body 132 and underlying strip substrate 134 arecut through with, e.g., a saw 168 along cutting lines 142, i.e.,perpendicular to a long side of strip substrate assembly 162, to definea plurality of individual memory cards 110 attached to carrier sheet 148and separated from each other by a width W of said cut (see FIG. 12).

In yet another possible embodiment (not illustrated), strip substrateassembly 162 can be encapsulated in a single-piece body of encapsulantand then cut into individual memory cards 110 using apparatus andmethods described in U.S. Pat. No. 5,981,314 to T. P. Glenn, et al.,which is incorporated herein in its entirety by this reference.

It may be noted that in embodiments requiring cutting, plastic body 132and/or strip substrate 134 can be precisely sawed through downwards froma top surface of plastic body 132 to, but not through, carrier sheet148, with currently available semiconductor wafer sawing equipment, andthat such cutting procedure simultaneously forms coplanar side walls 156and 158 on both severed plastic body 132 and severed substrate 112 ofeach memory card 110 where such sawing has taken place, as shownenlarged in FIG. 15. It may be further noted that, if a one-way keyingchamfer 130 is not molded into each memory card 110 duringencapsulation, as illustrated in FIG. 9, chamfer 130 can be preciselysawed into an appropriate corner of each card 110 after cards 110 areseparated from carrier sheet 148.

As will be apparent by now to those of skill in this art, manymodifications, variations, and substitutions are possible in thisinvention's methods and materials without departing from its spirit andscope. Accordingly, this invention's scope should not be limited by anyparticular embodiments illustrated and described herein, as these aremerely exemplary in nature. Rather, this invention's should commensuratewith that of claims appended hereafter and their substantialequivalents.

1. A memory card comprising: an insulative substrate comprising agenerally rectangular perimeter with four sidewalls, a first surfacewith circuit patterns thereon, and a second surface opposite the firstsurface, wherein the second surface includes a row of contacts alongonly a first one of the sidewalls of the substrate, the contacts beingelectrically coupled through the substrate to the circuit patterns ofthe first surface; a first semiconductor chip coupled to the firstsurface of the substrate and electrically coupled to the circuitpatterns by a flip chip connection, whereby the first semiconductor chipis electrically coupled to the contacts; and a body of a plasticencapsulant covering the first semiconductor chip, the first surface ofthe substrate, and at most three of the four sidewalls of the substrate,wherein at least one of the four sidewalls of the substrate is uncoveredby the plastic encapsulant and is coplanar with a sidewall of the bodyof the plastic encapsulant.